What is the best way to do this?

 

Take it off the bike before flushing it?

 

Remove the tank from the bike, then the petcock from the tank. Depending on how dirty the tank is, you may simply need to flush with water. If necessary, I sometimes add a squirt of engine degreaser, and flush again with clean water. I then take my time to remove all water from the tank using a wet / dry shop vacuum.

 

I'd use RO water so when it evaporates it doesn't leave sediment, but maybe that's nitpicking

 

Depends on how bad it is inside. Lots of vids on You Tube showing how to & what to use, depending on if it's just old gunk & bad gas or if it's rusted inside.

 

If you're referring to flushing out a bad liner... Do... Not... Bother. Just went through this and tried every suggestion on the forum. Get another tank on eBay if your liner is bad